Hot air gun



J. C. M MURRAY Aug. 27, 1940.

HOT AIR GUN Filed Jan. 18, 1958 V1 m m VMW mM 0 mm HM U W m k p by mv I111. i i x n 1%, 0V. NV. w. t fwm 13% mm mm 0 mm M aw um Q ow w -.m mu fi 0 m 9 0 w m m mm 3 w T g Patented Aug. 27, 1940 Z,Z12,fi94

HUT AER GUN John C. ltil'cl fiiurray, Winthrop, Mass. Application January 18, 1938, Serial No. 185,541 2 (Ci. MS -3S) This invention relates to a hot air gun and has to secure a greater efficiency in heating the air for one of its objects to provide a device of this w ll be presently described. kind which is simple and inexpensive to manu- Si dated within the rear end of the housing 7 facture and which can be easily operated. is rear it to the outer face of which is A further object of the invention to provide secured a fitting it which constitutes a valve an improved hot air gun which is so constructed housing for the control valve v. This fitting is that the handle and casing will not become heated formed with the valve chamber it and with an even when the device is used continuously. i1 .et port ll leading to the valve chamber and A still further object of the invention is to which communicates with a compressed air inlet provide an improved hot air gun which can be pipe l8. Said fitting is also provided with a 10 safely used in an atmosphere that is more or discharge duct it. The control valve, which is less loaded with combustible vapors. designated generally at 6, has a valve stem 28 Other objects of the invention are to improve scew threaded to the fitting i5 and provided generally hot air guns in the particulars more w h a valve portion 2i which controls the defully hereinafter set forth. livery of air through the delivery port E9. The In the drawing wherein I have shown a sestem 25} of this control valve extends through an lected embodiment of my invention; opening in the casing member i and is pro- Fig. 1 is a longitudinal section through a hot vided with a thumb piece by which it may be air gun embodying my invention; manipulated. Fig. 2 is a section on the line 22, Fig. l; Secured to the inside of the head i is a cylin- 20 Fig. 3 is a section through the casing on the der member 24- enclosing a cylinder chamber 25 line Fig. 2. with which the discharge duct l communicates.

My improved hot air gun comprises a front The cylinder is provided with discharge ports casing member i enclosing a heating chamber 2 2?? opening through its walls and situated within 535 in which is received an electric heating coil 3, said cylinder isa plunger 2'? which, when the hot 25 a rear casing member 4 which is provided with air gun is not in operation, occupies the full line a hollow pistol-grip handle 5 and which supposition shown in Fig. 1 thereby closing the disports a suitable air-control valve and a housing charge ports 25. member I connecting the two casing members i When the control valve 6 is opened, thereby to 3 and i and enclosing the autonatic switch by deliver compressed air to the cylinder chamber which the heating circuit is controlled. The t e p ss re f e a W force E116 plungcr housing member i is shown as made of sheet me- 2 f WaId nt t e do e H116 po n, a1 and is cylindrical form. forward end of thereby uncovering the ports 26 and the comsaid housing member fits within the circular pressed air will then pass from the cylinder flange 8 at the rear of the casing member 5 and chamber 25 through the ports 23 into the cham- 35 the rear end of said housing member '5' fits withber 28 within the housing member 1. The front in a circular flange 9 with which the casing head it is provided with ports or ducts 28 which member 4 is provided. provide a communication between the chamber Situated within the housing member l at its 23 and the heating chamber and, therefore, the it) forward end is a head or disk ill to which the compressed air which is admitted to the chamber 40 heating coil 3 is secured. This heating coil 3 23 will pass through these ports 29 into the is carried by a conical-shaped base it or" insulatheating chamber 2 where it will become heated ing material and said base is mounted on by pass ng C 1 he heating 00111 3. carried by a screw-threaded stem 52 which ex- Extending rearwardly from the head ill is a tends from the head it, said base being clamped rod or p 35, e n f whi h is re ived in a 4 to the head by the clamping nut 55 Which is recess 33 with which the plunger is provided, screw threaded to the stem. this post operating as a stop to limit the forward The front casing member 5 is conical in shape movement of the plunger when the compressed and at its small end it is provided with a hot air is admitted to the cylinder chamber 25. The delivery pipe it through which the heated air is screw-threaded member 52 by which the heating delivered. The conical base H, whi h is located coil is secured to the head iii may be made within the heating chambe 2, is secured to the integral with the post if desired. head ill with the smaller end thereof adjacent The plunger 2? is acted on by a spring 32 which the head and the larger end directed away from surrounds the post and which normally holds said head, the purpose of this arrangement being said plunger in its retracted position shown in 55 two contact full lines, Fig. 1, said spring yielding when compressed air is admitted to the chamber 25 and thereby allowing the plunger Z'i to move forwardly into a position to uncover the ports 26.

The heating circuit for the heating coil 3 is controlled by a switch which is automatically closed when the plunger 21 is moved forwardly into the dotted line position, Fig. 1, and which is automatically opened when the plunger is in its normal position shown in full lines, Fig. 1. By reason of this construction the movement of the plunger 21 from the full to the dotted line position, Fig. 1 by the compressed air admitted to the chamber 25 when the control valve 8 is opened, will not only open the discharge ports 26 and thus provide for the passage of the air through the chamber 28 and the heating chamber 2, but will also close the circuit to the heating unit so as to render the latter operative.

Mounted on the post 30 is a sleeve 33 of insulating material which bears at one end against the plunger Z'l and which is acted on by the spring 32. The switch mechanism for opening and closing theheating circuit comprises a contact ring 3 1 which is carried by the sleeve 33 and arms 35 and 33. The arrangement is such that when the sleeve 33 is in its retracted position shown in full lines, Fig. 1, the contact arms 35, 33 will be out of engagement with the contact ring 33 and will be resting against the sleeve 33, which is of insulating material, but when the plunger 25 is moved forwardly into the dotted line position, Fig. 1 then the contact sleeve 34 is moved into engagement with the contact arms 35, 36 and the switch will be closed. The heating circuit which includes the switch comprising the contact arms 35, 33 and the contact ring 33, includes the lead wires 31, 38 which are carried by a cable 39 that extends through the hollow handle 4. The lead wire 38 is connected to one end of a tie rod @3 which connects the two heads i4 and it! but is insulated therefrom as shown at 53 and the other lead wire 3'! connects to a second tie rod M which also connects the two heads I4 and ill but is insulated therefrom as shown at 52. The righthand end of the tie rod 3! is connected by a circuit wire 42 to one end of the coil 3 and the other end of said coil is connected to the contact arm 35 through the medium of a circuit connection 55 and a clamping screw 43 that is carried by the head H! but insulated therefrom as shown at M. The other contact arm 33 is connected to a circuit connection 35 through the medium of a clamping screw 43 that is carried by the head it but insulated therefrom as shown at 41, and the circuit connection 35 leads to and is connected to the tie rod fill.

So long as the plunger 21 and the contact ring 34 is in the full line position, Fig. l the heating circuit will be opened but when the control valve 3 is opened to allow compressed air to be admitted to the cylinder chamber 25, the plunger 2'! will be moved forward into the dotted line position thereby bringing the contact ring 34 into engagement with the contact arms 35, 36, thus closing the heating circuit. This same movement of the plunger 21 opens the discharge ports 26. When the switch 3 1, 35, 36 is closed as above described the heating circuit includes the lead wire 31, the tie rod M, the circuit connection 32, heating coil 3, contact arm contact arm 36, circuit connection 45, tie rod it, and leadwire 38.

35, contact ring 3%,

When the device is in operation the air under pressure will be delivered outwardly through the discharge ports 26 and there will thus be established in the chamber 28 a movement of air between the discharge ports 26 and the ports 29 as indicated by the dotted line arrows in Fig. l, the current of air flowing over the inner wall of the housing I. The flow of air in this way keeps the housing 1 cool and prevents the heat generated by the heating coil from being transmitted to the casing member 3.

Ihe arrangement of the heating coil with its small end toward the head It and the location of the ports 29 makes an extremely efficient heating unit because the air which is delivered through the ports 29 flows over the heated coil 3 for the full length of the latter. If desired the heating chamber 2 may be provided with a lining 8 of heat-insulating material.

From the above description it will be observed that the operation of my improved hot air gun involves simply the opening and closing of the control valve 3. To place the gun into use the control valve is opened to allow the compressed air to be delivered into the cylinder chamber 25, and the action of the compressed air against the plunger 2'5 will move the latter forward and thus not only open the discharge ports 26 but also close the switch 33, 35, 33 of the heating circuit, thus setting the heating coil in operation. This circuit will remain closed so long as the control valve is opened. To stop the operation of the heat gun it is only necessary to close the control valve for as soon as said valve is closed the delivery of air through the gun ceases and the spring 32 will return the plunger to its full line position and thus open the circuit of the heating coil. The control valve 3 also provides means for regulating the amount of air which is delivered through the gun. The spring 32 is so designed that even the delivery of a relatively small amount of air through the control valve will actuate the plunger and thus close the heating circuit. Since all the air which is passed through the gun to be heated is taken from a source of supply remote from the place where the gun is being used it will be safe to use the gun,

in an atmosphere which contains more or less combustible gas without the danger of creating an explosion which might occur if the air which waspassed through the heat gun and was heated thereby contained more or less combustible gas. This makes the tool especially desirable for use in garages. One use to which the device is admirably suited is for cleaning out the differential housing or transmission housing of an automobile when it is desired to change the lubricant in the differential or transmission. The delivery of the highly heated air into the differential housing or transmission casing under a high pressure serves not only to blow the lubricant contained therein out through the drain opening but the high heat of the air softens any hardened lubricant and renders it highly fluid so that it will readily drain from the housing.

The heat gun is also eminently suitable for delivering a hot air on the surfaces for purpose of drying them or drying some finish which has been applied to them.

I claim:

l. A hot air gun comprising a front casing member having a heating chamber therein, a rear casing member, a housing member situated between and connecting the casing members, the space within the housing member constituting an air circulating chamber, an apertured head forming a partition between the air circulating chamber and the heating chamber, an electric heating element carried by said head and situated within the heating chamber, a rear head at the rear end of the housing member, a fitting carried thereby and having an air passage for delivery of air to the air circulating chamber, a control valve to control admission of compressed air' to said passage, a cylinder member carried by said rear head and situated within the air-circulating chamber and adapted to receive the air delivered from the air passage, said cylinder' member having discharge ports leading to the air circulating chamber, a plunger in said cylinder normally closing the discharge ports into a position to open said ports circuit for the heating element, and a stop memcarried by the apertured head and serving to limit the forward movement of the plunger.

2. A hot air gun comprising a front casing tween and connecting the casing members, the space within the housing member constituting an air-circulating chamber, an apertured head forming a partition between the air-circulating chamber and the heating chamber, an electric heating element carried by said head and situated Within the heating chamber, a rear head at the rear end of the housing member, a fitting carried thereby and having an air passage for delivery of air to the air circulating chamber, a control valve to control admission of compressed air to said passage, a cylinder member carried by the rear head and situated to receive the air delivered from said air passage, said cylinder discharge ports leading to the pressure admitted to the cylinder member into a position to open said ports when the control valve is opened, a post carried by the JOHN C. MCMURRAY. 

